(a) Field of the Invention
The present invention relates to a method and apparatus for transmitting a packet in an optical transport network.
(b) Description of the Related Art
An optical transport network performs forward error correction (hereinafter, referred to as ‘FEC’) to enhance a transmission performance. In order to stably transmit a high speed signal that provides a high bandwidth in the optical transport network, ITU-T G.709 defines an optical channel transport unit (OTUk) and an optical channel data unit (ODUk) (k=1, 2, 3, 4). An OTUk includes an ODUk corresponding to information data including an optical channel payload unit (OPUk) and a parity byte for correcting an error of the ODUk. An area corresponding to the ODUk is referred to as an in-band area, and an area corresponding to the parity byte is referred to as an out-band area.
FIG. 1 is a diagram illustrating an example of the OTUk.
Referring to FIG. 1, the OTUk is formed with total 4 rows, and overheads are positioned at a first column to a sixteenth column. Overheads (FA OH) for aligning a frame are positioned at a first column to a seventh column of a first row, OTUk overheads are positioned at an eighth column to a fourteenth column of a first row, ODUk overheads are positioned at a first column to a fourteenth column of a second row to a fourth row, and overheads of the OPUk are positioned at a fifteenth column to a sixteenth column of entire rows.
OPUk payloads are positioned at a seventeenth column to a 3824th column (4*3808 bytes) of entire rows, and parity bytes for correcting an error are positioned at a 3825th column to a 4080th column (4*256 bytes) of entire rows.
An OTU1 has a bit rate of about 2.666 Gbit/s, an OTU2 has a bit rate of about 10.709 Gbit/s, an OTU3 has a bit rate of about 43.018 Gbit/s, and an OTU4 has a bit rate of about 111.8 Gbit/s.
In order to freely house a packet client signal while increasing a transmission efficiency in the optical transport network, a flexible ODU (ODUflex) signal is defined. The ODUflex signal includes, for example, ODUflex (GFP) for housing a packet client signal such as Internet Protocol version 4 (IPv4), Internet Protocol version 6 (IPv6), Multi Protocol Label Switching (MPLS), and Ethernet. The ODUflex (GFP) is a signal that encapsulates a packet client signal with a generic framing procedure (GFP) and that then GFP maps the packet client signal to an ODUflex payload and that adds an ODUflex overhead to the packet client signal. The ODUflex (GFP) can be multiplexed to a high order ODUk (HO ODUk) (k=2, 3, 4) of an order higher than the ODUflex (GFP) through a generic mapping procedure (GMP). In an ODU2, an ODU0, an ODU1, and an ODUflex are lower order ODUs. In an ODU0, an ODU1, and an ODU, an ODU2, an ODU3, and an ODU4 are high order ODUs.
In this case, a method and apparatus for transmitting a packet that can dynamically adjust a packet transport amount without packet damage is necessary.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.